The Wealth of Nations by Part 5 Chapter 1 Page 231

treated of as chiefly subservient to the happiness of a life to come. In the ancient philosophy the perfection of virtue was represented as necessarily productive, to the person who possessed it, of the most perfect happiness in this life.

In the modern philosophy it was frequently represented as generally, or rather as almost always, inconsistent with any degree of happiness in this life; and heaven was to be earned only by penance and mortification, by the austerities and abasement of a monk; not by the liberal, generous, and spirited conduct of a man. Casuistry and an ascetic morality made up, in most cases, the greater part of the moral philosophy of the schools. By far the most important of all the different branches of philosophy became in this manner by far the most corrupted.